Abstract: Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder that affects about 9%–13% of the general population. IBS is one of the main reasons to consult a primary care physician, and nearly 30% of visits to a gastroenterologist are for IBS. The diagnosis of IBS relies on subjective, patient-reported symptoms, thus making urgent the need for IBS-specific biomarkers. The same biomarkers, or perhaps different ones, can also be used to monitor disease evolution and response to treatment. A significant number of studies have looked in the immune system for establishing IBS biomarkers, based on the concept that IBS might represent a condition of immune dysregulation somewhere in the spectrum between health and inflammatory bowel disease. Such biomarkers can be detected in blood, intestinal biopsies, or luminal contents. Overall, results are rarely consistent between studies; small sample size, patient and disease heterogeneity, presence of comorbidities, and variation in sampling might contribute to these discrepancies. So far, studies have failed to provide a diagnostic immune biomarker for IBS, but they have considerably advanced our understanding of the disease pathophysiology, including the role of the individual's genetic make-up, and of the host–microbial interactions. High throughput analysis of a large number of well characterized patients holds promise for developing appropriate biomarkers for IBS.

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